NOx in exhaust gas discharged from a power station, various factories, vehicles and the like is the causes of photochemical smog and acid rain. As a method used to remove NOx efficiently, an exhaust denitration method utilizing selective catalytic reduction using ammonia (NH3) or the like as a reducing agent is used in wide fields including a thermal power station. As the catalyst, titanium oxide (TiO2) type catalysts using vanadium (V), molybdenum (Mo) or tungsten (W) as an active component is used. Particularly, catalysts containing vanadium as one of the active components not only have high activity but also is reduced in a deterioration due to impurities contained in exhaust gas and also can be used at lower temperatures. These catalysts are therefore currently used as main denitration catalysts (Patent Document 1). The catalyst is generally made into various forms such as a honeycomb-form and a plate-form upon use and also, various production methods of the catalyst have been invented and designed. Among these catalysts, net-like products obtained by processing a metal thin plate into a metal lath which is then coated with aluminum by flame coating and a catalyst structure obtained by a method in which using a ceramic fiber woven fabric or nonwoven fabric as a substrate, the above catalyst component is applied and pressure-bonded to the substrate to obtain a plate catalyst and then, the obtained plate catalyst is processed into an element having wave projections (spacer part) and the elements are stacked on each other have excellent characteristics that these catalysts are decreased in draft loss and are resistant to clogging with dust and burned ash of coal and are currently used in many denitration apparatuses for exhaust gas from the boiler of thermal power generation (Patent Documents 2 and 3).
In the meantime, as a method of producing a catalyst containing inorganic fibers relating to the above descriptions, many methods are known, these methods including a method in which a paste obtained by kneading a catalyst component with an inorganic fiber is applied in such a manner as to fill up the meshes of a metal lath (Patent Document 4), a method in which a nonwoven fabric sheet of ceramic fibers is impregnated with a catalyst component (Patent Document 5) and a method in which a ceramic fiber corrugated honeycomb support is made to carry a catalyst slurry (Patent Document 6). Also, as the latter method of producing a catalyst support by using an inorganic fiber nonwoven fabric sheet, many methods making use of paper-making technologies have been long known.    Patent Document 1: Japanese Patent Application Laid-Open No. 50-128681    Patent Document 2: Japanese Patent Application Laid-Open No 54-79188    Patent Document 3: Japanese Patent Application Laid-Open No 59-73053    Patent Document 4: Japanese Patent Application Laid-Open No 54-79188    Patent Document 5: Japanese Patent Application Laid-Open No. 2-169028    Patent Document 6: Japanese Published Examined Application No. 58-11253